August 2015
Intermediate to advanced
312 pages
7h 28m
Japanese
Content preview from 初めてのSpark
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.
273
C.3 対象アルゴリズムの概要
C-1
ムー
C.3.2
ALS
いフルタング
ALS
を用いた協調フィルタリングでは、行列因子分解（
Matrix Factorization
）によって、評価
値行列（ユーザー×アイテム）を、ユーザーとアイテムそれぞれの潜在的な特徴を表現した次元の
小さい行列に分解します。ここで、ユーザー特徴行列（ユーザー×
n
）とアイテム特徴行列（
n
×
アイテム）を得るために使用する手法が
ALS
（
Alternative Least Square
：交互最小二乗法）と呼
ばれています。
C-2
ALS
ALS
による行列因子分解の概要を
C-2
に示します。
2
つの特徴行列を同時に最適化すること
が難しいため、一方の行列を固定してもう一方を最適化する処理を、元の行列との誤差が収束する
まで繰り返し行うことにより、最適な特徴行列を求めます。
ALS
により、最適なユーザー特徴行
列（ユーザー×
n
）とアイテム特徴行列（
n
×アイテム）を求めたら、その
2
つの行列を掛け合わ
ユーザ
アイテム
ベ クト ル の
類似度算出
アイテム
アイテム
ユーザ
アイテム
ユーザ
アイテム アイテム
ユーザ
上位N件抽出
アイテム
×
アイテム
評価値行列
予測値行列 レ コ メ ンド
アイテム類似度行列
ユーザ ユーザ
アイテム
アイテム
アイテム特徴量行列
一方を固定してもう一方を最適化する処理を
目的関数が閾値以下となるまで繰り返す
評価値行列 ユーザ特徴量行列
ALS（Alternative Least ...
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Read now
Unlock full access
More than 5,000 organizations count on O’Reilly
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.